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Friday, 8 July 2016

Death of the Oceans

This
year, the tragic die-off of large volumes of coral at the treasured
Great Barrier Reef has provided a climate change shock like few
others. The cause was too much warm water — which seems to have
pushed the corals past a thermal survival threshold. And that warm
water, in turn, is tied to climate change.

Now,
however, a team of researchers has revealed that another Australian
coastal ecosystem that gets less attention — Australia’s
kelp-dominated Great Southern Reef, which covers a huge expanse along
its more temperate southern and southwestern coasts — saw an
equally dramatic ecosystem upheaval five years ago. And the cause was
the same — what the scientists call an “extreme marine heat
wave.”

“Some
of the same types of drivers are behind all of this, and I think this
really emphasizes the manifestation of these climate-driven events;
it’s more than just the coral reefs that are being affected by
this,” says Thomas Wernberg, a marine biologist at the University
of Western Australia who led the new research, which appeared
Thursday in the journal Science. Wernberg conducted the research with
21 other authors from a variety of institutions in Australia and
abroad.

Many
Americans will be familiar with the towering kelp forests off the
coast of California, where these enormous organisms can grow to be
more than 100 feet tall. The kelp off Australia’s southern and
southwestern coasts aren’t nearly as tall, but they are still the
backbone of a rich ecosystem, and the researchers refer to the
organisms as creating a “kelp forest.” Wernberg and his
colleagues estimate the Southern Reef as a whole to be worth $10
billion each year in economic terms due to tourism, fisheries and
other benefits.

But
in 2011, a surge of ocean temperatures between 3 and 5 degrees
Celsius above normal — conditions that for the kelp represented
“the hottest in recorded history, and that’s going back 215
years,” Wernberg says — took a devastating toll on a major part
of this ecosystem.

In
the most northern (in the Southern Hemisphere, the warmest)
latitudes, along the southwest coast of Australia south of Kalbarri,
kelp forests died in dramatic numbers, suggesting the temperatures
had “exceeded a physiological tipping point for kelp forests,”
the study reports.

“When
the heat wave happened, all of those northern kelp forests were
basically wiped out in a couple of months,” says Wernberg. “And
southwards, at least a couple-hundred kilometers, there were quite
substantial impacts, but you gradually got more and more kelps as you
went farther south.”

Here’s
a pair of before and after photos, taken by Wernberg, that show the
dramatic change:

The
study, based on years of underwater surveys, finds that before the
marine heat wave in late 2010, kelp covered around 70 percent of
reefs in the midwestern Australia coastal area — but afterward, in
2013, their area had declined by 43 percent, or 963 square kilometers
(371 square miles).

Moreover,
north of 29 degrees North latitude, kelp forests were gone entirely
or 90 percent decimated. This represented “a 100-kilometer range
contraction” as well as “functional extinction from 370 [square
kilometers] of reef,” the scientists report. (That’s 142 square
miles.)

And
it is not like the kelp then came back afterward or recovered.
Rather, the study reports that more tropical species of fish seized
the opportunity to colonize the warmer waters, including grazing fish
that ate kelp as it started to regrow. As a result, the ecosystem,
sparked by one extreme event, underwent what the scientists call a
“rapid climate-driven regime shift,” from which it simply may not
return unless the warming trend itself reverses.

“I
can’t remember having seen or heard about anything similar,”
Wernberg says.

Although
it does not perform a formal statistical attribution for the marine
heat wave, the paper clearly suggests this is all tied to climate
change, noting that the Indian Ocean, off Australia’s western
coast, is “a ‘hot spot’ where the rate of ocean warming is in
the top-10 percent globally.” Another such hot spot, incidentally,
has been off the U.S. East Coast in the Gulf of Maine, where
similarly dramatic effects have been observed.

“It
was extreme, so very rare by all accounts — I don’t believe it
was ‘natural,’ ” Wernberg wrote by email.

In
sum, we are starting to see that with certain very sensitive
ecosystems, temperature surges can have devastating and perhaps
irreversible effects. And one can argue this fits a key definition of
“dangerous climate change,” which turns on whether we are able to
stop the increase of greenhouse gases at a rate “sufficient to
allow ecosystems to adapt naturally.”

That
certainly doesn’t seem to be what happened in the kelp forests off
Australia’s western coast. “The future of kelp forest